1. Field of the invention
The present invention relates to a joint for connecting two duplex pipes each including an outer pipe and an inner pipe therein.
2. Description of the Related Art
As is well known, a duplex pipe is provided with an outer pipe for passing a first fluid and an inner pipe provided inside the outer pipe and for passing a second fluid. Being classified by manufacturing methods, there are two types of duplex pipes.
One type of a duplex pipe is made according to the following steps: the outer pipe and the inner pipe are prepared separately, and the inner pipe is inserted into the outer pipe; the outer pipe is squeezed so that projections formed on the inside wall of the outer pipe are pressed onto the surface of the outer wall of the inner pipe.
The other type is a duplex pipe made by integrally forming an outer pipe, an inner pipe and connecting ribs to connect the outer pipe and the inner pipe by extruding or drawing. In recent years, the duplex pipe of the latter type which integrally forms the outer pipe, the inner pipe and the connecting ribs is widely used in order to reduce the manufacturing costs.
In either of the types, a joint is necessary for connecting two duplex pipes, and the joint for duplex pipes requires to facilitate the connection work and reliability for preventing leakage.
Accordingly, it is an object of the present invention to provide a joint for duplex pipes that facilitates connecting work and achieves reliability in preventing leakage.
The object of the present invention is achieved by the following joints.
There is provided a joint for connecting a first duplex pipe to a second duplex pipe, each of the first and second duplex pipes including an outer pipe for passing a first fluid, and an inner pipe disposed inside the outer pipe, the inner pipe for passing a second fluid, the joint comprising:
a first outer pipe seal unit attached to an end of the outer pipe of the first duplex pipe;
a second outer pipe seal unit attached to an end of the outer pipe of the second duplex pipe;
a first inner pipe seal portion formed on an end of the inner pipe of the first duplex pipe;
a second inner pipe seal portion formed on an end of the inner pipe of the second duplex pipe;
a first sealing member disposed between the first outer pipe seal unit and the second outer pipe seal unit, the sealing member for sealing the outer pipes to prevent leakage of the first fluid;
a second sealing member disposed between the first inner pipe seal portion and the second inner pipe seal portion, the sealing member for sealing the inner pipes to prevent leakage of the second fluid; and
a connection structure for connecting the first and second duplex pipes, under a condition that the first sealing member is disposed between the first outer pipe seal unit and second outer pipe seal unit, and the second sealing member is disposed between the first inner pipe seal portion and the second inner pipe seal portion,
wherein a clearance between the first outer pipe seal unit and the second outer pipe seal unit is defined larger than a clearance between the first inner seal portion and the second inner pipe seal portion.
According to the invention, the first inner seal portion may be engaged with the second inner pipe seal portion.
According to the invention, the first sealing member and the second sealing member may be O-rings.
According to the invention, the radial thickness of the O-ring for the outer pipes may be larger than that of the O-ring for the inner pipes.
According to the invention, the hardness of the O-ring for the outer pipes, may be lower than that of the O-ring for the inner pipes.
According to the invention, one of the inner pipes may define a groove for accomodating the O-ring.
According to the invention, one of the first outer pipe seal unit and the second outer pipe seal unit may define a groove for accomodating the O-ring.
According to the invention, a bolt and a nut may form the connection structure.
According to the invention, the bolt may be inserted into the first outer pipe seal unit and the second outer pipe seal unit to fix the first outer pipe seal unit to the second outer pipe unit.
According to the invention, the first outer pipe seal unit may have a union nut portion and the second outer pipe seal unit may have a unit bolt portion engaged with the union nut of the first outer pipe seal unit to form the connection structure with the union nut portion and the union bolt portion.